Tropical Storm Philippe Forecast Discussion Number 6

By | September 24, 2023

WTNT42 KNHC 242040

Tropical Storm Philippe Discussion Number   6
NWS National Hurricane Center Miami FL       AL172023
500 PM AST Sun Sep 24 2023

Microwave and satellite data indicate that the center of Philippe 
has re-formed to the northeast of earlier estimates.  Overall, the 
storm is reasonably well organized, with convection near the center 
and a large central dense overcast.  Intensity estimates are about 
the same as the last cycle, so the initial wind speed remains 45 kt.

There aren't many changes to the intensity prediction reasoning in 
this advisory.  Increasing shear is forecast to otherwise counteract 
a conducive environment, leading to little net change with Philippe 
during the next couple of days.  Afterwards, models are in quite 
poor agreement on if the shear continues to rise to strong levels, 
which causes dissipation like the ECMWF, or if it becomes more 
manageable to allow for further intensification, similar to the 
GFS's hurricane forecast at day 5.  There are no obvious clues to 
the correct solution, and this is probably a very difficult forecast 
due to the feedback of Philippe's track affecting intensity, in 
addition to the inherent challenges of moderate shear cases. Thus, 
little change was made to the intensity forecast, which lies near 
the overall model and corrected-consensus aids.

The storm appears to be moving west-northwestward or 290/10 kt. The 
subtropical ridge to the north of Philippe is forecast to gradually 
weaken and slide eastward in a day or two, allowing the tropical 
storm to move more west-northwestward and northwestward by the 
middle of the week.  Uncertainty is large after that point, with the 
track very likely also dependent on the intensity and vortex depth, 
and the GFS and ECMWF models are on the opposite sides of the 
guidance envelope.  The long-range guidance has shifted a bit 
westward on this cycle, and the new forecast follows that trend.  
However, this forecast should be considered low-confidence in both 
track and intensity.


INIT  24/2100Z 16.8N  42.5W   45 KT  50 MPH
 12H  25/0600Z 17.3N  44.1W   45 KT  50 MPH
 24H  25/1800Z 17.8N  46.4W   45 KT  50 MPH
 36H  26/0600Z 18.2N  48.6W   45 KT  50 MPH
 48H  26/1800Z 18.8N  50.4W   45 KT  50 MPH
 60H  27/0600Z 19.7N  52.0W   50 KT  60 MPH
 72H  27/1800Z 21.0N  53.5W   50 KT  60 MPH
 96H  28/1800Z 23.0N  55.5W   55 KT  65 MPH
120H  29/1800Z 25.0N  57.0W   60 KT  70 MPH

Forecaster Blake

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